Conventionally, coating apparatuses using a rotary drum have been known as manufacturing apparatuses for medicine, food, and the like. For example, Patent Document 1 discloses an apparatus in which a rotary drum having a polygonal shape in cross-section (octagonal shape in this case) is rotated about a horizontal axis. Such a rotary drum is also referred to as a coating pan, and spray guns for supplying coating liquids are arranged in the drum. The spray guns are fixed to a support arm and the like installed in the drum, and are connected to air hoses and liquid hoses drawn-in from an outside of the drum. Powder and particle thrown into the rotary drum tumble in accordance with rotation of the drum. To surfaces of the rolling granular solids, coating liquids such as a sugar-coating liquid are sprayed from the spray guns. Simultaneously with spraying of the coating liquids, a hot air and a cool air are appropriately supplied into the rotary drum and exhausted therefrom. In this manner, formation and drying of coating layers are promoted.
When a sugar-coating process is performed in such a coating apparatus, first, objects to be processed as cores (such as tablets, hereinafter, the tablets are taken as a typical example) are housed in the rotary drum. After that, with the rotary drum being rotated, the coating liquids (sugar-coating liquid) and binder liquids are supplied into the drum so as to adhere to outer peripheries of the tablets. During the coating process, a hot air at approximately of from 50 to 100° C. is appropriately blown to the tablets. The hot air causes the sugar-coating liquid to be evaporated and solidified on the surfaces of the tablets so that the coating layers are formed. Then, operations of adding the coating liquids and then drying the same are repeated. Through the repetitive operations, the coating layers are laminated on the outer peripheries of the tablets again and again. In this manner, sugar-coating layers are formed.
Meanwhile, in such a coating apparatus, during the coating process, the sprayed coating liquids, raw materials of the granular solids, and the like enter a state of being floated by airflow in the apparatus. Thus, when the spray guns are arranged in an exposed state in the drum, in some cases, the floated coating liquids and granular solids may adhere to and accumulate on the spray guns. When contamination is increased by an increase in amount of adhering matters onto the spray guns, cleaning man-hours increase in accordance therewith. In addition, the adhering matters peel from the guns and fall in the drum so as to adhere to the tablets and the like, which causes deterioration such as an external appearance. Therefore, conventionally, as disclosed in Patent Document 2, there has been proposed an apparatus in which the spray guns are housed in a box-like case so that adhesion of floated matters onto the spray guns is suppressed and that washability is enhanced.
Further, with regard to the coating process, the coating layers formed on the tablets cause a tablet bed in the drum to vary in height. Accordingly, during the coating process, it is necessary to appropriately adjust positions of the spray guns so that a distance between the tablet bed and the spray guns are kept constant. Thus, conventionally, there has been proposed a coating apparatus having a structure in which the positions of the spray guns are vertically moved. For example, Patent Document 1 describes a structure in which the spray guns are vertically moved in an orthogonal direction with respect to a layer of an object to be processed, in other words, in directions of 45° with respect to the horizon so that the distance therebetween is maintained.    Patent Document 1: JP 2003-62500 A    Patent Document 2: JP 2573584 B    Patent Document 3: JP 08-173868 A    Patent Document 4: JP 2006-26592 A